Device for showing the distribution of the intensity in a neutron beam



March 3, 1942. 1 2,274,901

HARTMUT ISRAEL KALLMANN, FORMERLY KNOWN AS HARTMUT KALLMANN ET'AL DEVICE FOR SHOWING THE DISTRIBUTION OF THE INTENSITY IN A NEUTRON BEAM Filed Oct. 19, 1959 Patented Mar. 3, 1942 :J.

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DEVICE F OR SHOWING THE DISTRIBUTION OF THE INTENSITY IN A NEUTRON BEAM Hartmut Israel Kallmann, formerly known as Hartmut Kallmann, and Ernst Kuhn, Berlin, Germany, assignors to I. G. Farbenindustrie Berlin- Gharlottenburg,

Aktiengesellschaft,

Frankfort-on-the-Main, Germany, a. corpora-- tion of Germany Application October 19, 1939, Serial No. 300,277

In Germany October 19, 1938 1 Claim.

This invention relates to the art of investigation of substances with the aidof neutrons and isparticularly concerned with an improvement of a device io-rshovving the distribution of the intensity of a beam of neutrons. Neutrons excite fluorescent material either notat all or only very slightly. For obtaining a photographic or visible representation of a body or substance with theof the intensity of the neutron beam on the fluorescent material (as disclosed and claimed in our copending application Serial No. 197,928, filed March 24, 1938, now Patent No. 2,188,115, co-pending application Serial No. 270,354, filed April 2'7, 1939, and co-pending application Serial No. 298,336, filed October 6, 1939). It has been suggested to observe this image either visually or to cause the radiation proceeding from the fluorescent material to blacken a photosensitive layer brought into the immediate neighborhood of the 1 fluorescent mass thus fixing the image of the neutron beam photographically.

In most cases the device will be arranged in the following manner. One side of the fluorescent material is covered with said intermediate reaction layer, the side of the fluorescent mass is adjacent to the observer or the photosensitive layer respectively. In what follows this side is shortly designated as observers side.

One may suppose that the maximum possible radiation will be obtained at the observers side of the fluorescent material if the fluorescent material is chosen as thick as possible. Such thick layers are however unsuited in many cases. In

order to obtain sharp images of the distribution of the intensity the layer of the fluorescent material should, on the contrary, be as thin as possible, as the more the thickness of said layer increases the more the image of the distribution of the intensity of the neutron beam becomes these particles just excite the side of the fluorescent material being remote from the observer most strongly. In this case the radiation generated in the fluorescent screen and emerging towards the observer has to pass through the largest part of the material. If it is relatively thick a considerable part of said radiation will be absorbed or dispersed so that it can produce if at all only a diffused image on the observers side. For obtaining a bright and sharp image on the observers side of the fluorescent screen it is for these reasons by no means advantageous to make use of the thickest possible screen. Any how, there exists a most favorable thickness for said screen. It has been ascertained by tests that said thickness lies, in general, within a range in which the fluorescent screen itself absorbs only a small portion of the radiation generated in it.

According to the invention the intensity of the image on the observers side of the fluorescent screen can be considerably enlarged in that the radiation proceeding from the fluorescent material in the direction towards the side being remote from the observer is reflected right through the fluorescent screen to the observation side by means of a reflecting surface. Reflecting surfaces are quite generally used in optics for the utilisation of the light emitted to all sides by reflecting the light rays to a definite direction. The device designed in accordance with this invention can also be employed for showing the distribution of the intensity in a beam of quick neutrons. In the latter case a reaction layer must be used which emits, under the action of the quick neutrons, heavy particles, electrons or gamma rays that excite the fluorescent substance.

The reflection of the radiation emitted by the fluorescent screen can be effected in this way that the reaction layer applied to the fluorescent screen is formed as a mirror; it may for instance, be polished or provided with a suitable reflecting substance Or a substance able to be polished. It is under some circumstances, more advantageous to effect the reflection by the provision of a reflecting foil located between the reaction layer and the fluorescent material. The foil should be as thin as possible so that the particles exciting the fluorescent screen can penetrate the foil without undue absorption. In exciting fluorescent screens by heavy particles layers thinner than 0.001 mm., for instance, aluminium foils having a thickness of 0.0005 mm., have proved to be particularly suited for the purpose in View. In some cases it is however, still more advantageous not to form the surface of the reaction layer as a r tron source is conventionally indicated at l.

mirror but to make reflecting that side of the fluorescent screen which is adjacent to the reaction layer.

The reflecting surface can also be formed by the well known method of evaporation or disintegration.

The invention is now more specifically described with reference to the accompanying drawing in which the single figure schematically illustrates the device of the present invention and a mode of using the same. In the figure a neu- 2 is a part of these neutrons directed through the body or substance 3 being investigated. The device of the present invention is the combination, 4, 5, 6. 4 represents the reaction layer, 5 represents the reflecting layer, permeable by heavy charged particles, presenting a reflection surface and 6 represents a layer of fluorescent materials. "I designates a plate, permeable to the radiation proceeding from the fluorescent mass, which supports the whole system.

In use neutrons emerging from the body 3 being investigated encounter the layer 4 and there produce charged particles or gamma rays. These particles traverse the reflecting-layer 5 and energize the adjacent fluorescent mass 6. As the radiation proceeding from the fluorescent screen is the greater the more strongly the fluorescent screen is energized by the particles proceeding from the reaction layer under the action of the impinging neutrons the observer conventionally indicated at 8 will see an image of the body or substance 3 on the fluorescent screen. The radiation proceeding from the fluorescent screen towards the direction of the reaction layer is reflected by the reflecting surface 5 to the observation side of the fluorescent screen, thus enlarging the brightness of the image perceived by the observer.

If the radiation proceeding from the fluorescent screen is not visually observed, but is caused to darken a photographic layer, brought into the immediate vicinity of the screen, the sharpness of the image may be diminished by the support plate 1 located between the screen and the photographic layer. In this case it is more favourable to locate the support plate on the side of the reaction layer adjacent to the neutron source.

We claim:

A device for showing the distribution of the intensity in a neutron beam with the aid of a luminous substance and a neutron-reactive material which device consists essentially of a layer of a neutron-reactive material which emits heavy charged particles under the action of impinging neutrons, a layer of fluorescent material I permeable to light, and, between said two layers,

a lightreflecting layer which is permeable by said heavy charged particles. 

